Grass Land · Level 1-4 of 32
Bowser's first castle — a fiery, maze-like fortress with lava pits, moving firebars, and a boss fight at the end. The fake Bowser here is actually a Goomba in disguise. Duck under the axe to drop him into the lava.
Take the upper path past the firebars to skip a large section of the castle.
Hit the hidden block above the second lava pit for a Super Mushroom.